Review Request 128267: Include the Slab value in the Cached value

[David Edmundson]

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Ship it!




good research! 
Thanks.

Do you have commit access?

- David Edmundson


On June 20, 2016, 10:54 p.m., Rob Wu wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/128267/
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> 
> (Updated June 20, 2016, 10:54 p.m.)
> 
> 
> Review request for Plasma.
> 
> 
> Repository: ksysguard
> 
> 
> Description
> -------
> 
> Before this patch, Cached only counted the page cache.
> With this patch, the slab is also included. This change is visible
> through the APi in "mem/physical/application" and "mem/physical/cached".
> 
> 
> Why? For the calculation of used memory (`Appl`), the Slab should not
> be counted as used memory as it is a cache for kernel data structures.
> 
> free (from procps) calculates "Used" memory as follows:
> MemTotal - MemFree - (Cached + Slab) - Buffers
> (you can verify this using the numbers from `cat /proc/meminfo`).
> 
> This discrepancy in used memory was already noted before, at
> https://mail.kde.org/pipermail/plasma-devel/2008-December/002984.html
> 
> > This "Slab" value [1] is not available from the systemmonitor. It usually 
> > doesn't grow over 20MB at all anyway. I don't know how important this value 
> > is, so is it a feasable solution to simply ignore this and only show used, 
> > cache and buffer?
> 
> After 10 days of usage, my slab looks like this:
> 
> ```
> $ cat /proc/meminfo | grep Slab
> Slab:            2763208 kB
> ```
> 
> Clearly, the slab is non-negligible and should be deducted.
> 
> The immediate reason for writing this patch is that the "Memory Status"
> plasmoid displayed 4G of "memory usage" even after closing all programs.
> This was confusing, especially when `free -m` showed a much lower value.
> 
> 
> Diffs
> -----
> 
>   ksysguardd/Linux/Memory.c 6b2fcab 
> 
> Diff: https://git.reviewboard.kde.org/r/128267/diff/
> 
> 
> Testing
> -------
> 
> (on ArchLinux)
> 
> Add the "Memory Status" plasmoid to the desktop if is not already there.
> Note that the displayed value for "Physical memory" does not match the "Used" value as reported by `free -m`.
> 
> Build and install ksysguard after applying the patch:
> 
> ```
> cd build/
> cmake ../ -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr -DKDE_INSTALL_LIBDIR=lib -DBUILD_TESTING=OFF
> make
> sudo make install
> ```
> 
> Then restart plasmashell
> 
> 
> ```
> kquitapp5 plasmashell && kstart plasmashell
> ```
> 
> Look at the "Memory Status" widget on the desktop and observe that it displays a sensible value (similar to the "Used" value of `free -m`).
> 
> 
> Thanks,
> 
> Rob Wu
> 
>

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